Polar bears hunt seals by waiting near the edge of ice and waiting for the seals to surface. It’s especially crucial for mothers that have recently given birth to have access to the ice.

“A female goes into a maternity den when she’s pregnant in the fall and she stays in that maternity den until spring,” Laidre said. “And then she comes out of that den around March and she hasn’t eaten anything for 6-7 months … she comes out of that den with very small cubs and is very thin and needs to find food.”

In some parts of the Arctic, bears spend the ice-free months on land, where they’ll scavenge for food items like carcasses and bird eggs, but they’re “largely fasting” during those months, she said. In other parts where the ice doesn’t disappear completely, they follow the ice as it recedes north, over deeper water where fewer seals can be found.

Either way, it’s crucial that the bears build up their fat reserves while the ice is abundant and they have good access to prey.

Laidre noted that while “in some areas, the abundance of bears is linked to the sea ice,” in other locations the populations appear stable — for now. But even those populations will likely be in peril if rising temperatures — and shrinking sea ice — continues unchecked.

“If we look forward 50 to 100 years,” she said, “it’s really going to be a big problem for polar bears.”